1. Field of the Invention
The present invention relates to a charging unit that applies a charge bias for effectively charging a target member, a process unit including such a charging unit, and an image forming apparatus including such a charging unit. More particularly, the present invention relates to a charging unit that effectively charges an image carrying member with a given charge bias while being held in contact with the image carrying member, a process unit including such a charging unit therein, and an image forming apparatus including such a charging unit therein.
2. Discussion of the Related Art
Related art charging units generally include a charging member such as a charging brush member or a charging roller. Such related art charging units apply a given charge bias to the charging member so that the charging member can uniformly charge a surface of a target member that is disposed opposite to and in contact with the charging member.
A well known charge bias generally employed to apply to the charging member is an alternating current (AC) bias superimposed by a direct current (DC) bias.
The surface of the target member, before charging, may keep residual toner supplied onto an electrostatic latent image during a previous image forming operation. Specifically, when the residual toner for an electrostatic latent image still remains on the surface of the target member before charging, the potential deviation of the target member may be increased.
In such a case, a charge bias including a DC voltage cannot sufficiently remove the potential deviation. Unfortunately, this can easily cause a charging nonuniformity.
On the contrary, by repeating the charge and discharge during a short time period according to a potential deflection of an alternating component, the AC bias superimposed by the DC bias can reduce a production of such charging nonuniformity or potential nonuniformity.
However, such a charging unit can easily generate excessively charged parts on the target member. This may cause white spots or white deletions in which no image is formed.